The Palomar Abell Cluster Optical Survey. I. Photometric redshifts for 431Abell clusters

This paper presents photometric redshifts for 431 Abell clusters imaged as part of the Palomar Abell Cluster Optical Survey, of which 236 are new reds hifts. We have obtained moderately deep, three-band (Gunn gri) imaging for this sample at the Palomar Observatory 60 inch (1.5 m) telescope, as part o f the photometric calibration of the Digitized Second Palomar Sky Survey. O ur data acquisition, reduction, and photometric calibration techniques are described, and photometric accuracy and consistency are demonstrated. An em pirical redshift estimator is presented, utilizing background-corrected med ian g - r colors and mean g magnitudes for the ensemble of galaxies in each field. We present photometric redshift estimates for the clusters in our s ample with an accuracy of sigma(z) = 0.038. These redshift estimates provid e checks on single-galaxy cluster redshifts, as well as distance informatio n for studies of the Butcher-Oemler effect, luminosity functions, mass-to-l ight ratios, and many other projects.